**6. Assessment of arterial medial characteristics in carotid arteries using integrated backscatter ultrasound**

In general, atherosclerotic changes consist of two components: atherosis and sclerosis. According to a pathological study, these changes are recognized as thickening of intima-media thickness (IMT) which is associated with structural atheromatous changes and decreased

**Figure 5.** Representative histological images of carotid media. (A) (C) Histological images stained by elastic van Gieson staining. (B) (D) Digitized images, in which elastic fibers were selected by the following thresholding of the digital im‐ age LUZEX F (Nireco, Kyoto, Japan). (B) Elastic fiber index: 59.3 %, Elastic fragmentation index: 57.7 % and IBS value: 9.1 dB. (D) Elastic fiber index: 18.9 %, Elastic fragmentation index: 79.3 % and IBS value: 14.4 dB.

extensibility which is associated with functional sclerotic changes in elastic and collagen fibers. There are several ultrasound parameters to evaluate atherosclerosis, such as IMT, which is associated with atheromatous plaque formations and stiffness ß, which are associated with decreased extensibility of the arterial wall. IMT measurement is widely performed for the detection of atheromatous lesions and associated with age and coronary risk factors [21, 22]. However, IMT is not always associated with the severity of arterial sclerosis in patients with hypertension [23]. This may be due to the degenerative changes in the medial smooth muscle cells and variably increased amount of elastin and collagen in hypertensive vessels [24].

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The elasticity of major arteries is also affected by cardiovascular risk factors such as hyper‐ tension, hyperlipidemia, diabetes and aging. Stiffness ß, which was defined by Hayashi et al was found to be independent of blood pressure in the physiological range and associated with the severity of coronary atherosclerosis [25-27]. An increase in arterial stiffness has been reported as an early sign of atherosclerosis [28]. Therefore, it is very important to evaluate arterial sclerosis non-invasively. We showed that IBS values of carotid media were correlated with the stiffness of carotid arteries, and those were also correlated with elastic fiber fragmen‐ tation index (Figure 5) [29].
